This disclosure relates to integrated circuit devices, and more specifically, to a method and structure to improve the conductivity of via structures in semiconductor devices.
In semiconductor circuits, it is common to connect the devices fabricated in or on a semiconductor substrate with a metallic interconnection structure made of metal lines and “vias” which interconnect the metal lines. Conventionally, the metal lines are arranged in horizontal layers, i.e. parallel to the substrate, and separated by layers of dielectrics while vias are disposed vertically in openings in the dielectric to interconnect the layers of metal lines. In such a structure, the bottoms of the vias are typically flat where they contact the upper surfaces of the underlying metal lines.
As the dimensions of the interconnection structure have become smaller, it has become a challenge to provide an adequate via contact. The contact resistance between the vias and metal lines has increased as the contact area between the vias and the metal lines has decreased due to the smaller diameter of the vias. In the prior art, a “via gouging” process has been adopted to achieve an adequate contact resistance. In the via gouging process, rounded or conical “gouges” are produced in the tops of the underlying metal lines. This has the effect of producing a rounded or conical bottom to the vias which descend lower than the top surface of the underlying metallurgy.
While the via gouging process is effective in improving contact resistance, the plasma sputtering typically used to produce the feature also damages the dielectric surface over which upper layers of metallurgy are deposited. This has the effect of degrading these metal layers and deleteriously affects the reliability of the interconnect structure, and therefore, the integrated circuit in which it is incorporated.
Thus, producing an improved via structure with improved conductivity without the damage caused by the via gouging process is desirable. The present disclosure presents a method and structure to address this problem.